The present invention relates to a method for manufacturing white light source, especially to a method for manufacturing high-brightness white light source by ultraviolet light source and suitable phosphor.
A white light source is generally provided by mixing light source of different wavelength. For example, a conventional white light source can be realized by mixing red light, green light and blue light with suitable intensity ratio. Alternatively, the white light source can be realized by mixing yellow light and blue light with suitable intensity ratio. The conventional method for manufacturing white light source can be summarized as following:
In a first prior art of white light source, three LED dies based on InGaAlP, GaN and GaP are packaged into a lamp and emit red light, blue light and green light, respectively. The light emitted from the lamp can be mixed by a lens to provide white light.
In a second prior art of white light source, two LED dies based on GaN and GaP are functioned to emit blue light and yellowish-green light. The blue light and yellowish-green light are mixed to provide white light. The white light sources according to above-mentioned two approaches have efficiency of 20 lm/W.
A third prior art of white light source is proposed by Nichia Chemical co., wherein an InGaN based blue LED and a yellow YAG phosphor are used to provide the white light source. This white light source requires uni-color LED to provide white light at the expense of smaller efficiency 15 lm/W. Moreover, the phosphor is a mature art and commercially available.
A fourth prior art of white light source is proposed by Sumitomo Electric Industries Ltd., and uses a white-light LED based on ZnSe. A CdZnSe thin film is formed on the surface of a ZnSe crystalline substrate. The CdZnSe thin film is functioned to emit blue light and the ZnSe crystalline substrate emits yellow light after receiving the blue light of the CdZnSe thin film. The blue light and the yellow light are mixed to provide white light. In this approach, only one LED chip is required and the operation voltage thereof is 2.7 V, smaller than the 3.5 V operation voltage of the GaN based LED. Moreover, no phosphor is required.
In a fifth approach to provide white light source, an ultra-violet LED is used to excite a plurality of phosphors such that the phosphors luminesce light of different colors for mixing into a white light.
In first and second prior art white light source, LEDs for multiple colors are required. The color of the white light source is distorted if one of the LEDs malfunctions. Moreover, the driving voltages for LEDs of different colors are also different; this complicates the design of driving circuit.
The third prior art white light source employs complementary color to achieve white light. However, the white light produced in this way has no uniform spectral distribution (especially in 400 nm-700 nm) as the natural white light such as sunlight. The white light thus produced has relatively poor chroma, which is, even indistinguishable to human eyes, differentiable to instrument such as camera. Therefore, the color rendering property and reproducing ability are not satisfactory and this white light source is used mainly for lighting.
The fourth prior art white light source has the drawbacks of low luminescent efficiency (only 8 lm/W) and short lifetime about 8000 hours.
In fifth prior art white light source, it is preferable to use three phosphors for emitting three different colors to enhance color rendering property. However, the phosphors should be prudently chosen to have absorption band matched with the wavelength of the exciting radiation. Moreover, the phosphors should have compatible absorption coefficients and quantum efficiency to provide white light of high quality. Those requirements place a strict constrain to the materials of the phosphors.
It is the object of the present invention to provide a method for manufacturing high-brightness white light source by ultraviolet light source and suitable phosphor. The emission spectrums of the phosphors after being excited by the ultra-violet radiation source should cover the wavelength regimes of red light (585-640 nm), green light (500-570 nm) and blue light (430-490 nm).
In one aspect of the present invention, the method for manufacturing white light source includes the steps of providing an ultra-violet light as radiation source; and preparing two kinds of phosphors each receiving the ultra-violet light and emitting light of different wavelength.
In another aspect of the present invention, one phosphor is designated to emit light covering two wavelength regimes of three primitive colors, and another phosphor is designated to emit light covering remaining wavelength regime of the three primitive colors. The phosphors are mixed in predetermined ratio such that the lights of different wavelength are combined to provide a white light.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which: